1. Field of the Invention
The present invention relates to a carrier-attached copper foil, a laminate, a laminate producing method, a printed wiring board producing method, and an electronic device producing method.
2. Description of Related Art
A printed wiring board is typically produced through processes that involve bonding an insulating substrate to a copper foil to produce a copper-clad laminated board, and forming a conductor pattern by etching the copper foil surface. As miniaturization of electronic devices continues and the need for higher performance increases, there has been progress in the development of a high-density mounting technique for mounting components, and a technique for achieving high signal frequency. This has created new requirements for printed wiring boards, including fine (fine pitch) conductor patterns, or accommodation of high frequencies.
In order to meet the fine pitch requirement, a copper foil having a thickness of 9 μm or less, or a smaller thickness as thin as 5 μm or less is needed. Such ultrathin copper foils have poor mechanical strength, and easily break or produce wrinkles during production of a printed wiring board, and there has been an emergence of a carrier-attached copper foil that uses a thick metal foil as a carrier, and in which an ultrathin copper layer is electrodeposited on the carrier via a release layer. The ultrathin copper layer is laminated to an insulating substrate, and, after the thermocompression of these two layers, the carrier is released and removed via the release layer. Circuit patterns are formed on the exposed surface of the ultrathin copper layer using a resist, and a predetermined circuit is formed.
The resin bonding surface of the ultrathin copper layer in the carrier-attached copper foil mainly needs to have sufficient peel strength between the ultrathin copper layer and the resin base, and the peel strength needs to sufficiently remain even after treatments and processes, such as high-temperature heating, wet processes, soldering, and chemical treatments. In a typical method of improving the peel strength between the ultrathin copper layer and the resin base, large numbers of roughening particles are attached to the ultrathin copper layer after creating a large surface profile (irregularities, roughness) on the ultrathin copper layer.
However, a problem occurs when such an ultrathin copper layer having a large profile (irregularities, roughness) is used for a semiconductor package substrate, which requires a particularly fine circuit pattern compared to other printed wiring boards. Specifically, unwanted copper particles remain after etching the circuit, and this causes problems such as insulation failure between circuit patterns.
WO2004/005588 discloses a carrier-attached copper foil for fine circuits, including semiconductor package substrates. Specifically, this publication attempts to use a carrier-attached copper foil that is produced without roughening a surface of an ultrathin copper layer. Because of its low profile (irregularities, degree of roughness, roughness), the unroughened ultrathin copper layer tends to have poorer adhesion (peel strength) for resin than a common copper foil for printed wiring boards. This carrier-attached copper foil thus needs further improvements.
JP-A-2007-007937 and JP-A-2010-006071 describe providing a Ni layer and/or a Ni alloy layer, providing a chromate layer, providing a Cr layer and/or a Cr alloy layer, providing a Ni layer and a chromate layer, and providing a Ni layer and a Cr layer on the surface of a carrier-attached ultrathin copper foil that comes into contact with (or is bonded to) a polyimide resin substrate. By providing such surface treatment layers, these publications achieve the desired bonding strength between the polyimide resin substrate and the carrier-attached ultrathin copper foil, without a roughening treatment, or with a limited (finer) roughening treatment. These publications also describe performing a surface treatment with a silane coupling agent, or performing an antirust treatment.
The previous efforts to develop a carrier-attached copper foil had a primary focus on the peel strength between an ultrathin copper layer and a resin base. For this reason, there are not many studies concerning a carrier-attached copper foil suited for high-density mounting on a printed wiring board, and there is a room for further improvements.
The integrated circuit density of a printed wiring board is typically improved by forming a laser hole, and connecting the inner layer and the outer layer through the hole. A method that forms a fine circuit involving a fine pitch uses a technique called MSAP (Modified-Semi-Additive-Process), whereby an ultrathin copper layer is etched away with a sulfuric acid-hydrogen peroxide etchant after forming a wiring circuit on the ultrathin copper layer. Laser drillability through the ultrathin copper layer is therefore important in the fabrication of a high-density integrated circuit substrate. Laser drillability through the ultrathin copper layer is involved in a variety of conditions such as hole size accuracy, and laser output, and greatly affects the design and the productivity of an integrated circuit. Japanese Patent No. 3261119 describes a copper-clad laminated board having desirable laser drillability. However, studies by the present inventors found that further improvements are needed in terms of etchability.